Re: [APML]: What is Adaptive Optics?

[barber@sbig.com (Michael Barber)]

Chuck Vaughn wrote:

>If I understand this correctly AO replaces the function previously performed
>by the autoguider in the ST-7 or ST-8. In other words you're not autoguiding
>and performing AO at the same time (two independent systems)?

This was the original design, and with good drives the this is true.  There
was no reason to correct the telescope drive while using the AO because the
periodic error was completely eliminated by the corrections of the AO during
the exposure.  This required the coils driving the AO's mirror to have a
range of travel that was enough to encompass the total error found in most
drives.  However, when measuring the total range of correction in the final
production prototypes we found that the range was not as great as we would
have liked and might not be good enough for drives that had significant
periodic error that wasn't trained out some other way (PEC, etc.).  So we
implemented a feature that will "bump" the drive as needed to keep the guide
star away from the edge of the correcting mirror.  This is a much grosser
correction than autoguiding corrections and is used only to be sure the
guide star stays within the AO's range of travel.  The benefit is that it
will now eliminate the PE of just about any drive no matter how bad it is,
so long as it is capable of being controlled by an autoguider. 

Regards,
Michael Barber
SBIG